Gravity simulation doesn't work (Cloth Simulation)
I'm a little new to Blender, so I don't know if this will help, but you can also try checking the Gravity in the Scene Properties tab.  According to the Blender documentation, the default setting should be -9.810 to simulate Earth's gravity.
Good Luck!
Source:
https://docs.blender.org/manual/en/latest/physics/forces/gravity.html